Many military training facilities do not have sufficiently large areas to accommodate the range of standard small caliber ammunition. Since small caliber ammunition are particularly easy to launch in an unintended direction, a safety hazard may exist. Bullets are often well outside of partially enclosed training ranges thereby endangering others. To prevent this from occuring barriers have to be constructed or the shooting range has to be further extended at substantial cost. Thus, a projectile with limited range as hereinafter described would have both economic and safety advantages. For good simulation personnel experience and safety, it is desirable to have the training ammunition ballistically match the performance of standard ammunition to the maximum range of interest and then fall well short of the range of standard ammunition. It is also important to have a training round which is not only similar in appearance but one that is also inexpensive to manufacture.
Prior art limited range training rounds frequently failed to provide realistic training because they did not ballistically match the standard ammunition, their light weight precluded firing from an automatic weapon, their range was not adequately limited, and they were often expensive to manufacture. The desired maximum range of a training round fired from a service rifle is approximately two hundred meters. Inadvertently firing a rifle at an angle higher than intended by as little as ten degrees will result in a service round range of thousands of meters.
In the past, prior art statically unstable training rounds have been designed to be first gyroscopically stable by spin and then destabilized with either forward or aft mounted aerodynamic surfaces that dampen spin. The problem with the aforementioned was that they were unpredictably sensitive to varying atmospheric conditions and minor manufacturing part tolerance variations. When fired in a low density atmosphere, these prior art devices retain their gyroscopic stability for a longer distance thus flying to a longer range than desired. However, in a high density atmosphere they differ ballistically from the service ammunition at the target range.
Some prior art statically stable limited range training rounds depend on super caliber aerodynamic surfaces and therefore require the use of a sabot which increases their cost. Other prior art training rounds use high drag aerodynamic surfaces to limit their range. This precludes ballistic match to the range of interest. These prior art designs are expensive and not suitable for an automatic rifle.
Prior art devices for limited range training projectiles which utilize a Mach number dependent transition from static stability to static instability usually have no fins to generate high yaw drag. The aforementioned training round would be unsuitable for rifled barrels since it requires a relatively small spin rate to be gyroscopically stable, thus it would continue in undesired low drag long range flight. Also, this type of training round is limited to launch at a particular Mach number.